1. Field of the Invention
The present invention relates to an X-ray photographing apparatus having a frontal side photographing system positioned to face the frontal side of an object, e.g., a human body to be photographed and a lateral side photographing system positioned to face his lateral side.
2. Description of the Related Art
Recently, X-ray photographing apparatuses of a bi-plane type, which can photograph an object in various directions, have been proposed as X-ray photographing apparatus used for examination of the circulatory system of the human body, for example.
The photographing apparatus of this type has a frontal side photographing system for photographing the human body from his frontal side and a lateral side photographing system for photographing him from his lateral side and is enable to photograph the human body from two different directions, i.e., from his frontal and lateral sides at the same time.
The frontal side photographing system has a first semicircular (or C-shaped) arm supported by a support shaft which is supported by a base on the floor and extends parallel to the floor. An X-ray tube and an image intensifier (which will be hereinafter referred to as I.I) are rotatably mounted on both ends of the arm, respectively, and opposed to each other. In photographing, the X-ray tube and I.I are adjusted in position so that their central axes are aligned with each other.
The lateral side photographing system has a second semicircular arm which is attached to a support shaft extending perpendicular to the support shaft for the frontal side photographing system. The shaft for the second arm is supported by the ceiling through a carriage which is linearly movable in longitudinal and width directions of the human body to be photographed. An X-ray tube and an I.I are mounted on both ends of the second arm to oppose to each other. When photographing is to be performed, they are adjusted to align their center axes with each other.
When the human body is to be photographed from two directions at the same time, using these photographing systems, they are usually positioned at their normal positions. At their normal positions, they are positioned in such a way that X-ray beams emitted from the X-ray tubes cross each other and that the crossing point or iso-center comes to a reference position where the iso-center coincides with centers of curvature of the first and second arms. When they are under this state, the direction of the X-ray tube and I.I of the frontal side system with respect to the human body is adjusted, by rotating the first arm about its support shaft in LAO (left anterior oblique projection) or RAO (right anterior oblique projection) direction while rotating it about its curvature center in CAU (caudal) or CRA (cranial) direction. Similarly, the direction of the X-ray tube and I.I of the lateral side system is adjusted, by rotating the second arm about its support shaft in CAU or CRA direction while rotating it about its curvature center in LAO or RAO direction. During the above adjustment, the position of the iso-center does not change.
Positions of these X-ray tubes and I.Is are furthrr adjusted relative to the human body, depending upon what his part is to be photographed, by moving the second arm in his longitudinal or width direction by the carriage while moving the first or second arm in a direction perpendicular to the floor by means of its lifter. In this case, the iso-center is shifted from the reference position.
During each of the adjusting processes, each of the arms is moved independently of the other. This creates the possibility that the arms interfere with each other to damage themselves. In order to prevent the interference between the arms, there is provided X-ray photographing apparatuses which have an interference preventing function.
This interference preventing function of the conventional X-ray photographing apparatuses, however, is intended to meet only the case where the first and second arms are rotated in CAU and CRA or RAO and LAO directions, while the arms are held at their normal positions or keeping the iso-center consistent with the reference position. When the first and second arms are rotated while they are out of their normal positions or the iso-center is shifted from the reference position, therefore, their interference cannot be prevented with reliability.